Electronic amplifiers



June 1955 H. T. J. WIEGERINCK 2,712,066

ELECTRONIC AMPLIFIERS Filed May 26, 1952 SUPPLY Mfll/V INPUT BATTERY/i7.Y

Inventor HENDRIKUS THEODORUS Iosem WIEGERmcK Attorney 2,712,066Erncraonrc AMPLnunns Eendrikus Theodorus Joseph Wiegerinek, Cambridge,England, assignor to Pye Limited, Cambridge, England, a British companyApplication May 26, 1952, Serial No. 290,002

Claims priority, application Great Britain June 1, 1951 7 Claims. (Cl.2Sll27) The present invention relates to electronic amplifiers and moreparticularly to radio receivers which may be operated either from thesupply mains or batteries, and are of the kind which comprise a numberof filamentary type electron tubes, including a filamentary type outputtube which is used as the output tube during operation from thebatteries, and an indirectly-heated cathode type output tube which isused as the output tube during operation from the supply mains and hasits heater supplied by the supply mains, and in which during operationfrom the supply mains the filament current for the filamentary typeelectron tubes is derived from the H. T. supply through the cathode typeoutput tube and during operation from the batteries the filament currentof all the tubes which are then in operation is supplied from batteries.

Known receiver arrangements of this kind suffer from the disadvantage,when operating from the supply mains, that fluctuations in the supplymains voltage causes variations in the current through the cathode typeoutput tube and hence variations in the filament current of thefilamentary type electron tubes fed therefrom. Since the filamentcurrent for the filamentary type electron tubes, which are of thedirectly-heated type, should be kept constant within small limits toavoid damage to the tubes, these filament current variations,particularly if they cause an increase over the rated filament currentfor a tube tend to shorten the life of the filament, or if the increaseis sufficiently great the filament or filaments will burn out.Conversely if the variations cause a reduction in the filament currentto below the rated value, a deterioration of the performance of thereceiver will result. Variations in filament current may also occur ifthe cathode type output tube has to be replaced, since small differencesin characteristics may occur between different tubes of the same type.

It is an object of the present invention to overcome this disadvantageand provide an arrangement whereby when operating from the supply mainsthe filament current of the filamentary type electron tubes may be keptsubstantially constant and independent of fluctuations in the supplymains voltage.

To this end, according to the present invention, in an electronicamplifier and more particularly a radio receiver of the kind described,a D. C. connection is provided between a grid of the cathode type outputtube and a load connected in series with a preceding valve, whenoperating from the supply mains, whereby a D. C. bias voltage developedacross said load may be applied to the cathode type output tube tocontrol its conductance to compensate for fluctuations of the supplyvelt age and so that the filament current supplied to the filamentarytype electron tubes through said cathode type output tube remainssubstantally constant.

Preferably, the D. C. connection is made between the signal grid of thecathode type output tube and the anode of the preceding tube, which isnormally acting as an L. F. amplifier stage, the D. C. voltage beingdeveloped across the anode load of the preceding tube and serving2,712,066 Patented June 28, 1955 as a bias voltage on the signal grid ofthe cathode type output tube to control the current flow therethrough.For operation from batteries, the connection from the anode of thepreceding L. F. amplifier to the grid of the filamentary type outputtube, which is then in use, is made through a condenser.

Preferably the filamentary type electron tubes have their filamentsconnected in series in such a manner that the filament of anyfilamentary type electron tube which is not in use when operating fromthe supply mains, for example the filamentary type output tube, may beswitched out of circuit.

In a preferred form of the invention, the series connected filamentsdraw their current supply from the cathode type output tube through aresistor connected in series with the cathode of that tube, thisresistor being preferably of the type having non-linear characteristicwhich further assists in maintaining the filament current to theremaining filamentary type electron tubes at the correct value. Ifdesired this resistor may be made variable or be pres-set to facilitatein the initial adjustment of the filament current. For this resistor,the heater of the cathode type output tube could be used in someapplications. A large condenser is connected across the resistor andseries connected filaments to filter out audio frequency variations inthe cathode current of the cathode type output tube.

In order that the invention may be more fully understood, reference Willnow be made to the accompanying drawing which shows the basic circuitarrangement of a radio receiver constructed in accordance with thisinven' tion.

This receiver is constructed with filamentary type electron tubes V1,V2, V3, and V4, having their filaments connected in series. Duringoperation from batteries the filaments of these tubes are supplied fromthe battery B. The tube V4 represents the filamentary-type output tubeand tube V: is a low-frequency amplifier feeding this valve. Tubes "1and V2 represent preceding stages in the receiver. An indirectly heatedcathode type output value V5 is also provided which fulfils the functionof the filamentary type output valve V4 during operation from the supplymains, when the filament of the filamentary type output tube V4 isswitched out of circuit by the switch S4. The anode of the tube V3 isconnected through a resistor R3, to the signal input grid of the tube V5which is in use when operating from the supply mains, and is alsoconnected through the condenser C3 to the signal input grid of the tubeV4 which is in use when operating from batteries. The filament h of thetube V5 is supplied from the supply mains and the filaments of theremaining tubes V1, V2 and V3, when operating from the supply mains, areconnected between the cathode of the tube V5 and the H. T. negative lineand supplied with current derived from the cathode high tension supplythrough the mains type output tube V5 in a known manner. A nonlinearresistor R1 is connected in series with the cathode of the cathode typeoutput tube V5 and the filaments of the battery type tubes V1, V2 andV3, to provide the appropriate negative grid bias for the tube V5. Alarge condenser C1 is connected from the cathode of tube V5 across theresistor R1 and the series connected filaments of tubes V1, V2 and V3 toby-pass the audio frequency variations in the current of the cathodetype output tube V5, and the current fed through the resistor R1 to thefilaments of tubes J1, V2 and V3 is therefore substantially free from A.C. components. The screen grid of the tube V3 is fed from a tappingpoint on the resistor R1, during operation from the supply mains, whichtends to improve the power regulation, and during operation frombatteries the screen grid of this tube is fed through the resistor R2connected to the positive H. T. supply line from the H. T. battery, theconnection to the resistor R1 being broken by the switch S3. Duringoperation from the supply mains, the H. T. supply for the tubes V1 andV2 is derived from the junction of the resistor R1 and the cathode ofthe tube V5 and during operation from batteries the H. T. supply tothese tubes is derived through the dropping resistor R4. This changeoveris effected by the switches S5 and S6. The tubes V3 and V4, or V3 and V5are supplied from the battery or mains H. T. supply respectively bysuitable operation of the switches S1, S2 and S6.

The various switches shown form different sections of a multi-polarswitch, operated by a single control, hte arrangement being such thatduring operation from batteries the switches S2, S4 and Se are closedand the switches S1, S3 and S5 are open. For operation from the supplymains, as shown in the drawing the switches S2, S4 and S6 are open; andthe switches S1, S3 and S5 are closed.

The action of the bias circuit will now be explained. During operationfrom the supply mains, an increase in current through the tube V5 due toan increase in supply voltage tends to cause an increase in heatercurrent through the preceding tubes V1, V2 and V3, which are lamentarytype electron tubes and thereby cause the filament emission of thesetubes to increase. This increased filament emission causes the tubecurrent to rise and in the case of the tube V3 produces a greatervoltage drop across the load resistor R5 connected in series with theanode of this tube. Since the anode of the tube V3 is directly coupledto the signal input grid of the output tube V5, the voltage across theresistor R5 is applied as a bias to the signal input grid of the tubeV5, and the increased voltage drop across resistor R5 thereforeincreases the bias applied to the grid of the tube V5 and tends todecrease the current flowing therethrough and thereby maintains thefilament current flowing through the preceding filamentary type electrontubes V1, V2 and V3 at its correct value. Conversely if the currentthrough the cathode type output tube V5 decreases from its normal value,due to fluctuation in the supply voltage, the emission of the tubes V1,V2 and V3 tends to decrease, reducing the tube current and hence thevoltage dropped across the load resistor R5. This decreases the biasapplied to the signal input grid of the tube V5 and allows this tube todraw more current, thus again maintaining the filament current of thebattery type tubes V1, V2, V3 at the correct value.

The cathode potential of the tube V5 is arranged to be of such a valuethat although the signal grid of this tube is connected to the H. T.supply through the resistor R5 no grid current normally flows in thetube V5 and the tube is able to operate as an output tube working on thenormal part of its characteristic. This cathode potential is determinedby the value of the resistor R1, and the voltage drop across the heatersof the tubes V1, V2 and V3.

It will be understood that only the basic circuit arrangement has beendescribed, and that other switches will be provided to switch thecircuit connections between the electrodes of tube V4 and tube V5 whenchanging from battery operations to rnains operation and vice versa.

Whilst a particular embodiment has been described, it will be understoodthat various modifications may be made without departing from the scopeof the invention. For example the bias voltage may be derived from anearlier stage in the receiver or amplifier, instead of from the L. F.amplifier feeding the output tube as above described.

In a further modification the bias voltage may control the conductanceof the cathode-type electron tube by applying this voltage to thesuppresser grid instead of to the signal input grid.

I claim:

1. Electronic apparatus which may be operated from supply mains andbatteries, comprising a plurality of filamentary type electron tubes,and a cathode type electron tube having a heater, a cathode and at leastone grid electrode, and having its heater supplied from the supplymains, a battery for supplying filament current to said filamentary typeelectron tubes during operation from batteries, a source of high tensionvoltage for said filamentary type electron tubes during operation frombatteries, a source of high tension voltage for said tubes duringoperation from supply mains, means connecting the filaments of at leastsome of said filamentary type electron tubes in series with the cathodeof said cathode type electron tube during operation from the supplymains, whereby the filaments of said filamentary type electron tubes aresupplied from the current flowing through said cathode type tube, aresistive load connected in series with the anode of one of saidfilamentary type electron tubes and a direct current connection betweensaid resistive load and a grid of said cathode type electron tube duringoperation from supply mains.

2. Electronic apparatus which may be operated from supply mains andbatteries, comprising a plurality of filamentary type electron tubes,and a cathode type electron tube having a heater, a cathode, and atleast one grid electrode, and having its heater supplied from the supplymains, a battery for supplying filament current to said filamentary typeelectron tubes during operation from batteries, a source of high tensionvoltage for said filamentary type electron tubes during operation frombatteries, a source of high tension voltage for said tubes duringoperation from supply mains, means connecting the filaments of at leastsome of said filamentary type electron tubes in series with the cathodesof said cathode type electron tube during operation from the supplymains, whereby the filaments of said filamentary type electron tubes aresupplied from the current flowing through said cathode type electrontube, a resistive load connected in series with one of said filamentarytype electron tubes and a direct current connection between saidresistive load and a grid of said cathode type electron tube, duringoperation from supply mains.

3. Electronic apparatus which may be operated from supply mains andbatteries, comprising a plurality of filamentary type electron tubes, atleast one of said filamentary type electron tubes having a screen grid,and a cathode type electron tube having a heater, a cathode, and atleast one grid electrode and having its heater supplied from the supplymains, a battery for supplying filament current to said filamentary typeelectron tubes during operation from batteries, a source of high tensionvoltage for said filamentary type electron tubes during operation frombatteries, a source of high tension voltage for said tubes duringoperation from supply mains, means connecting the filaments of at leastsome of said filamentary type electron tubes in series with the cathodeof said cathode type electron tube during operation from the supplymains, whereby the filaments of said filamentary type electron tubes aresupplied from the current flowing through said cathode type electrontube, a resistive load connected in series with a filamentary typeelectron tube having a screen grid, a direct current connection betweensaid resistive load and a grid of said cathode type electron tube,during operation from supply mains and a direct current connectionbetween the cathode of said cathode type electron tube and the screengrid of the said filamentary type electron tube in series with saidresistive load.

4. Electronic apparatus which may be operated from supply mains andbatteries, comprising a plurality of filamentary type electron tubes, atleast one of said filamentary type electron tubes having a screen grid,and a cathode type electron tube having a heater, a cathode, and atleast one grid electrode and having its heater supplied from the supplymains, a battery for supplying filament current to said filamentary typeelectron tubes during operation from batteries, a source of high tensionvoltage for said filamentary type electron tubes during operation frombatteries, a source of high tension voltage for said tubes duringoperation from supply mains, means connecting the filaments of at leastsome of said filamentary type electron tubes in series with the cathodeof said cathode type electron tube during operation from the supplymains, whereby the filaments of said filamentary type electron tubes aresupplied from the current flowing through said cathode type electrontube, a resistive load connected in series between the anode of afilamentary type electron tube having a screen grid and the high tensionpositive supply linue, a direct current connection between the anode ofsaid filamentary type electron tube having a screen grid and a grid ofsaid cathode type elec tron tube during operation from supply mains, anda resistor connected between the cathode of said cathode type electrontube and the screen grid of said filamentary type electron tube which isin series with the resistive load.

5. Electronic apparatus which may be operated from supply mains andbatteries, comprising a plurality of filamentary type electron tubes, atleast one of said filamentary type electron tubes having a screen grid,and including a filamentary type output tube having at least one gridelectrode, and used as an output tube during operation from batteriesand a cathode type electron tube having a heater, a cathode, and atleast one grid electrode and having its heater supplied from the supplymains, and used as an output tube during operation from the supplymains, a battery for supplying filament current to said filamentary typeelectron tubes during operation from batteries, a source of high tensionvoltage for said filamentary type electron tubes during operation frombatteries, a source of high tension voltage for said tubes duringoperation from supply mains, means connecting the filaments of at leastsome of said filamentary type electron tubes in series with the cathodeof said cathode type electron tube during operation from the supplymains, whereby the filaments of said filamentary type electrcz tubes aresupplied from the current flowing through said cathode type electrontube, a resistive load connected in series between the anode of afilamentary type electron tube having a screen grid and the high tensionpositive supply line, a direct current connection between the anode ofthe said filamentary type electron tube having a screen grid and a gridof said cathode type electron tube and a non-linear resistor, betweenthe cathode of said cathode type electron tube and the screen grid ofthe said filamentary type electron tube in series with the resistiveload.

6. Radio receiving apparatus which may be operated from supply mains andbatteries, comprising a plurality of filamentary type electron tubes,including a filamentary type output tube used as an output tube duringoperation from batteries and a cathode type electron tube having aheater, a cathode, and at least one grid electrode and having its heatersupplied from the supply mains, and used as an output tube duringoperation from the supply mains, a battery for supplying filamentcurrent to said filamentary type electron tubes during operation frombatteries, a source of high tension voltage for said filamentary typeelectron tubes during operation from batteries, a source of high tensionvoltage for said tubes during operation from supply mains, meansconnecting the filaments of at least some of said filamentary typeelectron tubes in series with the cathode of said cathode type electrontube during operation from the supply mains, whereby the filaments ofsaid filamentary type electron tubes are supplied from the currentflowing through said cathode type electron tube, a resistive loadconnected in series with one of said filamentary type electron tubes anda direct current connection between said resistive load and a grid ofsaid cathode type electron tube during operation from supply mains.

7. Radio receiving apparatus which may be operated from supply mains andbatteries, comprising a plurality of filamentary type electron tubes, atleast one of said tubes having a screen grid and including a filamentarytype output tube used as an output tube during operation from batteriesand a cathode type electron tube having a heater, a cathode, and atleast one grid electrode and having its heater supplied from the supplymains, and used as an output tube during operation from the supplymains, a battery for supplying filament current to said filamentary typeelectron tubes during operation from batteries, 2. source of hightension voltage for said filamentary type electron tubes duringoperation from batteries, a source or" high tension voltage for saidtubes during operation from supply mains, means connecting the filamentsof at least some of said filamentary type electr'on tubes in series withthe cathode of said cathode type electron tube during operation from thesupply mains, whereby the filaments of said filamentary type electrontubes are supplied from the current flowing through said cathode typeelectron tube, a resistive load connected in series between the anode ofa filamentary type electron tube having a screen grid and the hightension positive supply line, a direct current connection between theanode of the said filamentary type electron tube having a screen gridand a grid of said cathode type electron tube, and a non-linear resistorconnected between the cathode of said cathode type electron. tube andsaid screen grid of the said filamentary type electron tube in serieswith the resistive load.

References tilted in the file of this patent UNlTED STATES PATENTS

